Metallurgical furnace



D. BAIRD.

METALLURGICAL FURNACE.

APPLICATION FILED JUNE 17, 1920.

1,375,346. Patented Apr. 19, 1921.

W lTN E 35 ES INVENTOR 7 a Jam :1 3mm AITORNEYS' UNITED STATES PATENT OFFICE.

DUDLEY BAIRD, OF BERKELEY, CALIFORNIA, ASSIGNOR T GENERAL CHEMICAL COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

METALLURGICAL FURNACE.

Specification of Letters Patent.

Patented Apr. 19, 1921.

Application filed June 17, 1920. Serial No. 389,702.

' ments in Metallurgical Furnaces, of which the following is a specification.

This invention relates to metallurgical roasting furnaces of the type employing a series of hearths so arranged that the treated material falls successively from hearth to hearth.

The invention has for an object to provide an improved arrangement for introducing air into the furnace whereby a more effective and more complete combustion or oxidation may be obtained.

(Jertain flotation concentrates and other sulfur-poor ores cannot be successfully roasted in furnaces of the type commonly in use in which air is introduced over the ore bed of the hearth without the addition of eX- traneous fuel to maintain a suflicient temperature. I have found that the difiiculty is due in part to the failure to obtain intimate or complete contact between the oxygen and the ore particles, particularly in the lower hearths. The difficulty will be understood when it is considered that the fresh air introduced is considerably diluted bymixture with the gases already in the furnace, and poor in oxygen, before it comes in contact with the ore particles, and further that the air can, at best, come in contact. only with that portion of each particle forming the exposed surface of the fuel bed.

The present invention provides an apparatus in which the fresh air preferably preheated is so introduced that while still in fresh and substantially undiluted condition it comes in direct and intimate contact with the ore particles as they fall from one hearth to another. This arrangement is advantageous not only because the ore contacts with air undiluted by the furnace gases and preferably heated, but also because the whole surface of each ore particle is exposed to such air.

The principle of the invention will best be understood by reference to a specific embodiment. For the purposes of illustration, the invention will be described with reference to its application to a circular roasting furnace having a vertical series of superposed hearths communicating successively at their centers and rims.

In the drawing forming a part of this speclfication, the figure is a central sectional view of a roasting furnace embodying the invention. The furnace shown is of well known type comprising a plurality of superposed hearths 1, 2, 3, i, 5, 6, 7, communicating alternately at their rims and centers by means of passages 8, 8 at the circumference of alternate hearths and central openings 9., 9 at the centers of the remaining hearths. The furnace is provided with the usual fine 10 and preferably also with the usual air inlet 11 at the bottom of the furnace. Rabble arms 13 carried by a rotatable vertical shaft 14, are provided for stirring the ore upon the hearths and for feeding it toward the communicating passages, as is usual practice. The rabbles of the rabble arms are not shown in the drawing since these are of usual construction and representation thereof would add nothing to the clearness of the disclosure.

Air is circulated through the rabble arms l3'to cool the arms and to heat the air, and such heated air is introduced into the furpace for combustion purposes.

As shown, an air pipe 15 centrally positioned in the shaft 1% supplies air to the rabble arms through tubes 16. The rabble arms at their inner ends open into the shaft 14 as indicated at 17 so that the air heated during its circulation through the rabble arms enters the annular space between the shaft 14 and air pipe 15. From this space some or all of this heated air is introduced into the combustion chambers of the furnace by the means which form the object of my invention. In the particular embodiment shown, oppositely located openings 18, 19 are provided in the central shaft above hearths 5 and 7 in substantially the same vertical plane as the rabble arms 13 which stir the ore upon hearths 4 and 6. Short tubes 20, 21 forming air conduits are mounted in front of such openings, the length of the tubes being such that the outer ends thereof are immediately behind the streams of ore falling through the openings 9, 9 of hearths 4 and 6 so that air blown through such tubes will impinge directly upon such ore. The length of the tubes should not be so great as not to permit'the air to be blown directly into the falling ore, that is, the tubes should not extend as far as the edge of the hearth'above; on the other hand, the tubes may be somewhat shortened if desired, as

long as the pressure of the air flowing from the openings is suiiicient to enable a large proportion of the air .to reach the falling body of ore. To a certain extent, therefore, a shortening of the tube may be compensated by a corresponding increase in air pressure without changing the amount of air brought into contact with the falling ore, and to such extent, therefore, such shorter tube may be the mechanical equivalent of a tube having its outer end immediately behind the streams of falling ore. The tubes 20 are shown as of smaller diameter than the tubes 21 for the reason that in the particular construe tion illustrated it was desired to introduce a greater supply of air over the hearth 7.

The tubes 20, 21 preferably are made removable and interchangeable so that tubes of various sizes may be applied as circumstances may require. As shown, each tube is provided at its upper edge with an inwardly directed flange 23 which engages a corresponding flange 24 formed at the upper edge of the corresponding opening in the shaft 14 to hold the tube removably in position. I r

In the described construction, the air will be introduced into a substantially continuvous stream of ore particles falling from naces embodying the invention, much better combustion is obtained because of the more intimate and complete contact between the ore particles and the fresh, undiluted and preferably preheated air introduced through the. tubes. For this reason certain flotation concentrates, which are relatively poor in sulfur, can be roasted effectively and expeditiously in such furnaces, whereas, in furnaces as heretofore constructed, roasting of such ores was made possible only by the introduction of extraneous fuel.

The invention is not limited in scope to its application to furnaces of the type illus trated but may be applied. to furnaces of various other types by making provision for the mixing with falling ore, of air in. fresh and undiluted condition in such manner that the fresh and undiluted air Sill'l'OHl'KlS the ore particles and intimately contacts therewith. The invention may of course, be applied to one hearth only of a mult-iple hearth furnace, and to a plurality of such hearths.

-VVhen I speak in my specification of ore I intend to include material. other than ore which may be subjected to heat treatment in a multiple hearth furnace.

I claim:

1. In. a metallurgical furnace the combination with a plurality of hearths and means for causing a stream of material to fall from one hearth to another, of an air conduit whose exit end is so positioned that, when the furnace is in operation, said end is immediately behind said stream, thus being adapted to direct a blast of air into contact with the falling material.

2. In a metallurgical furnace having a plu 'ality of superposed communicating hearths, the combination with a rabble arm for causing a stream of material to fall from one hearth to another of an air conduit whose exit end is so positioned that, when the furnace is in operation, said end is immediately behind said stream, thus being adapted to directa blast of air into contact with the falling material.

In a metallurgical furnace having a plurality of superposed communicating hearths, the combination with a rabble'arm for causing a stream of material to fall from one hearth to another of an air con duit whose exit end is so positioned that, when the furnace is in operation, said end is immediately behind said stream, thus being adapted to direct a blast of air into contact with the falling material, said air conduit being positioned substantially in the plane of the rabble arm.

4:. In a circular metallurgical furnace having a plurality of superposedhearths communicating successively at their centers and rims, the combination with a rotatable vertical shaft, an air pipe therein and a rabble arm constructed to receive air from said air pipe and discharge it into said shaft, of an air conduit communicating with the interior of said shaft, the outer end of said conduit being so positioned that, when the furnace is in operation, said end is immediately behind said stream, thus being adapted to direct a blast of air into contact with the falling material.

5. In a circular metallurgical furnace having a plurality of superposed hearths conununicating successively at their centers and rims, the combination with a rotatable vertical shaft, an air pipe therein and a rabble arm constructed to receive air from said air pipe and discharge it into said shaft, of an air conduit communicating with the interior of said shaft, the outer end of said conduit being so positioned that, when the furnace isin operation, said end is immediately behind said stream. thus being adapted to direct a blast of air into contact with the falling material, said air conduit being positioned substantially in the plane of the rabble arm.

In testimony whereof I have hereunto set my hand.

DUDLEY BAIRD. 

